1. Field of the Invention
The present invention relates to a communication control apparatus for connecting a plurality of slave stations to a master station via a communication network so as to transfer data between the master station and the plural slave stations, in which the plural slave stations are arranged by a servo amplifier control apparatus for controlling a servo motor and a main shaft motor, and by a main shaft amplifier control apparatus, whereas the master station is arranged by a numerical control apparatus.
2. Description of the Related Art
In the conventional communication control apparatus, the following communication control method has been introduced. That is, a single master station is provided with respect to a plurality of slave stations. To synchronize a plurality of slave stations with the single master station, the batch transmission frame is transmitted in the batch mode from the master station to the plural slave stations, and then the slave stations which receive this batch transmission frame can be synchronized with the master station.
In other words, the control timing of the respective servo amplifiers is synchronized with the control timing of the main shaft amplifier in response to the communication start code of the batch transmission frame transmitted from the master station. Based upon the synchronized reference timer, the slave stations start the transmissions to the master station at different timing with respect to the ID numbers of the respective slave stations.
Such a conventional communication control apparatus is described in, for example, Japanese Laid-open Patent Application No. 4-293338 opened in 1992.
In the above-explained conventional communication control apparatus, the very precise timing controls could not be performed, but very lengthy time periods are necessarily required in order that the master station receives the frames transmitted from all of these slave stations. The reason why such very precise timing controls could not be realized is given as follows: Upon sensing the batch transmission frame sent from the master station, each of these slave stations resets the timing synchronizing counter employed in the own slave station. When the count value of this timing synthesizing counter reaches a certain defined value (the defined values are different from each other in the respective slave stations), the slave station produces the transmission initiation signal used to transmit the frame to the master station. If the very precise transmission initiation timing is determined, then the circuit scale of the comparators for comparing the defined values and the counter values of the timing synchronizing counters is increased. As a consequence, there is a problem that the circuit scales of the slave stations are increased. This solution could not be practically accepted.
The present invention has been made to solve the above-explained problem, and therefore, has an object to provide such a communication control apparatus capable of shortening idle time during which each of slave stations does not perform a transmission to a master station in order to achieve a maximum transfer efficiency within a limited bandwidth of a network used to connect the master station to a plurality of slave stations based upon such a judgement that the shorter the response time from the plural slave stations to the master station becomes, the better the communication control can be realized.
In a communication control apparatus, according to an aspect of the present invention, in which a batch transmission frame is transmitted in a batch mode from a master station to a plurality of slave stations, and individual response frames are transmitted from the respective slave stations to the master station, when a batch transmission frame containing a transmission order designation of the slave stations from the master station is previously transmitted, and also the respective slave stations respond to the master station, response frames are successively transmitted in a continuous manner to the master station based upon the transmission order designation transmitted from the master station every time the transmission of the response frame by the slave station prior to the own slave station is completed.
Also, according to the communication control apparatus of the present invention, the response frame transmission from the slave station to the master station is switched at specific timing based upon reference counters provided within the slave stations, the timing phases of which are made coincident with timing phase of the master station, and also a station number of a predetermined slave station.
Also, according to the communication control apparatus of the present invention, the master station previously makes a recognition as to which slave station is connected to a network by executing an initialization communication.
Also, according to the communication control apparatus of the present invention, when the transmission is carried out from the slave stations to the master station, the master station executes the transmission order designation in such a manner that a confirmation is made as to whether or not a terminator indicative of a final end of a daisy chain connection is connected to which slave station based on the transmission frame transmitted by the slave station, and the transmission is commenced by such a slave station which is connected to the final end separated from the master station by the farthest distance.
Also, according to the communication control apparatus of the present invention, while utilizing shortening of the transmission time from a plurality of slave stations to the master station, the master station shortens an interval for producing an interrupt signal to a microcomputer for executing a data process operation in the master station in order to shorten a series of communication cycle between the master station and the plural slave stations.
Also, according to the communication control apparatus of the present invention, transmission start timing of such a slave station which firstly executes a frame transmission to the master station is commenced in predetermined offset time based upon a timing synchronizing counter which is synchronized with the batch transmission frame from the master station to the plurality of slave stations.
Furthermore, according to the communication control apparatus of the present invention, transmission start timing of such a slave station which firstly executes a frame transmission to the master station is commenced in predetermined offset time designated by data contained in a transmission order designation from the master station to the slave stations based upon a timing synchronizing counter which is synchronized with the batch transmission frame from the master station to the plurality of slave stations.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawing.